The field of liquid crystals has witnessed a remarkable breakthrough, thanks to a research team led by Dr. Jialei He from Nagoya University’s Graduate School of Engineering. By developing a novel method to process cholesteric liquid crystals (CLCs) into micrometer-sized spherical particles, the team has revolutionized the applications of liquid crystals in various fields. The findings of their study, recently published in Advanced Optical Materials, shed light on the potential of using these spherical CLC particles for anti-counterfeiting measures and other innovative applications.
Cholesteric liquid crystals (CLCs) have long fascinated scientists due to their resemblance to natural structures like the iridescent wings of butterflies and the glossy coating on beetles’ exoskeletons. These natural structures exhibit captivating colors and properties, which researchers have sought to replicate in the lab. CLCs owe their mesmerizing colors to their unique molecular structure and optical properties. Their helical arrangement and the pitch, the vertical distance between each loop, determine the wavelengths of light they selectively reflect, resulting in a diverse range of colors. Furthermore, the color displayed by CLCs can change depending on the viewer’s orientation to the helix, offering endless color possibilities.
To harness the potential of CLCs more effectively, researchers have focused on developing spherical CLC particles. These particles, with a three-dimensional matrix containing the helical structure, allow for better control over their coloration. However, the size of these particles has posed a significant challenge. Current methods produce spherical CLC particles that are 100 micrometers in size, rendering them unsuitable for many applications. Overcoming this obstacle, Dr. Jialei He and Dr. Yukikazu Takeoka from Nagoya University, along with their colleagues, employed a technique called dispersion polymerization. By carefully selecting a mixture of solvents, the researchers successfully created micrometer-sized spherical CLC particles. This breakthrough was not without its challenges, as the softness of the samples at room temperature made the testing phase complex. Nonetheless, the team managed to develop uniform-sized monodisperse spheres, ensuring a controlled particle size distribution.
The development of micrometer-sized spherical CLC particles holds immense promise for a range of applications. One such application is the creation of more secure QR codes that are resistant to replication. Capitalizing on the property of chirality, which refers to the inability of CLCs to be superimposed onto their mirror image, the researchers combined the colors of spherical CLC particles with non-chiral pigments readily available in the market. This ingenious technique resulted in the generation of an anti-counterfeiting QR code that can only be decrypted when a specific circular polarizer is employed. The circular polarizer allows the non-chiral light to pass through while blocking the chiral light emitted by the QR code. Dr. Yukikazu Takeoka emphasizes that this breakthrough opens up new possibilities for creating low-cost structural color functions that differ from conventional color materials. Apart from anti-counterfeiting measures, these micrometer-sized spherical CLC particles have extensive applications that leverage their circularly polarized structural colors with minimum angle dependence.
Dr. Jialei He’s research team has made a groundbreaking contribution to the field of liquid crystals with their development of micrometer-sized spherical particles from cholesteric liquid crystals. By addressing the size limitations of existing methods, the team has unlocked new opportunities for applying CLCs in anti-counterfeiting measures and other domains. The extraordinary optical properties of CLCs continue to captivate scientists and engineers, offering boundless possibilities for future advancements in the field. As research in liquid crystals progresses, it is exciting to envision the innovative applications that will emerge, driven by the unique properties and capabilities of CLCs. With each breakthrough, the boundaries of what is possible with liquid crystals are pushed further, paving the way for a promising future of technological advancements.
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